The invention relates to a gear pump with at least two delivery gears meshing with one another, whose gear teeth tip circles intersect at crossing points on both sides of a plane containing the gear axes and whose teeth form a pressure zone in front of said plane in the rotation direction of the delivery gears, and a suction zone behind said plane in the rotation direction. The pressure zone communicates with a kidney/cardioid shaped pressure chamber. A pressure line communicates with the pressure chamber. The suction zone extends beyond the intersection of the tip circles on the suction side in the rotation direction of the delivery gears, and communicates with a kidney/cardioid shaped suction chamber. A suction line communicates with the suction chamber. A feed zone is located behind the suction zone in the rotation direction of the delivery gears, said feed zone being fillable by excess pumping medium delivered by the gear pump through a channel under pressure and/or at an increased flowrate.
A gear pump of this type is the subject of German Patent Document DE 29 33 493 A1. The feed zone is connected with the pressure side of the pump and serves to fill with pumping medium the cavitation bubbles that appear particularly at higher pump rotational speeds, and thus to avoid implosion of the cavitation bubbles in the vicinity of a pressure zone, said implosion being associated with disturbing noises and dangerous pressure waves.
In accordance with German Patent Document DE 29 33 493 A1, an injector jet can be provided in the suction line in the flow direction upstream of the suction chamber, said jet likewise allowing pumping medium to be admitted from the pressure side of the pump. This is intended to improve the filling of the tooth spaces of the delivery gears with pumping medium at the suction zone. Clearly, cavitation bubbles cannot be avoided, so that these bubbles must be filled in the feed zone.
An object of the invention is to improve further a gear pump of the type described above.
This object is achieved according to the invention by virtue of the fact that the suction chamber that extends beyond the intersection on the suction side of the tip circles of the delivery gears is connected at that point with the feed zone.
The invention is based on the general idea of completely avoiding the formation of cavitation bubbles and not merely filling cavitation bubbles that form afterwards. By linking the suction chamber and feed zone, an area extending in the rotation direction of the delivery gears is obtained for filling the tooth spaces with pumping medium.
This clearly increases the pressure in the transitional area between the suction chamber and the feed zone, since the tooth spaces, which in the rotation direction of the delivery gears are located behind the intersection of the head circles of the delivery gears on the suction side, are supplied with delivery medium at an increased rate and/or at an increased pressure. As a result, complete filling is achieved.
The gear pump according to the invention therefore acts firstly as a delivery pump that supplies pumping medium to a consumer, and secondly as a charging pump which acts to fill the delivery spaces by creating a high flowrate or an increased pressure.
Since the gear pump according to the invention can operate free of cavitation even at very high rotational speeds, especially quiet operation is achieved because the pressure waves that would otherwise appear when the cavitation spaces coincide in the pressure zone of the pump are completely avoided.
By eliminating these pressure waves, the material stress on the pump elements is also clearly reduced so that the lifetime of the gear pump can be increased and materials less able to withstand loads, which are therefore less expensive, may be used.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.